1. Field of the Invention
The invention relates generally to the field of substrate treating, and more specifically, to aqueous bleaching solutions with optically functional nanoparticles for providing functional benefits to the bleaching solution and/or a treated substrate, wherein the optically functional nanoparticles are stable to degradation and settling in the aqueous bleaching solutions.
2. Description of the Related Art
Bleaches are used for cleaning purposes such as stain removal, whitening, disinfecting, sanitizing, sterilizing, and the like. Bleaches may also be used during laundering to bleach stubborn stains and dirt, as well as to achieve whitening and brightening of fabrics, particularly of white and light-colored textiles and materials. Conventional bleaches include an aqueous solution of an oxidant such as sodium hypochlorite, coloring agents, whiteners, and the like.
However, ensuring that a stable and visually pleasing color is achieved in an aqueous bleaching solution containing an oxidant is difficult. This may be attributed to the fact that particulate materials such as dyes, pigments and whiteners either degrade due to oxidation or do not form stable dispersions and settle out of solution.
Existing methods for providing a stable aqueous bleaching solution include the use of oxidation-resistant pigments and dyes, either alone or encapsulated. Examples of these oxidation-resistant pigments include inorganic pigments such as tramline blue (UMB), cobalt blue, iron oxide, and the like. These pigments are chemically compatible with the oxidants but they do not form stable dispersions and settle out of solution quickly. Hence, the aqueous bleaching solutions containing these pigments require the use of thickening agents and flocculants to form gel-like structures to suspend these pigments. Further, the encapsulation of these pigments, with subsequent dispersion in the source of oxidant necessitates a careful balancing of densities and electrostatic charges in order to resist precipitation and particle agglomeration in the aqueous bleaching solutions. U.S. Pat. Nos. 6,420,328, 6,448,215, 6,503,877, 6,624,134, 5,688,435, 4,708,816, 4,931,207, 4,952,333, 5,104,571, 4,623,476, 4,271,030 describe the use of such pigments and are herein incorporated in their entirety as references.
Existing methods also suggest the use of certain water-soluble inorganic compounds such as chromium or permanganate salts, which are compatible with the oxidants, to impart color to the aqueous bleaching solutions. These water-soluble inorganic compounds may be used to form yellow or purple solutions. However, aqueous bleaching solutions containing these inorganic compounds do not have the desired aesthetics.
U.S. Pat. Nos. 4,714,562 and 5,089,162 disclose dyes for use in liquid dishwasher detergents that have less than 3 percent sodium hypochlorite and high concentrations of builders and other ingredients. However, such dyes have limited utilization to simply increasing the yellow color of the aqueous bleaching solutions.
U.S. Pat. No. 4,474,677 describes halogenated copper phthalocyanine pigments for forming blue or green aqueous bleaching solutions. However, the stability of the blue bleaching solutions is rather limited. These halogenated copper phthalocyanine pigments release copper ions when they degrade, which tend to catalyze the decomposition of the sodium hypochlorite present in the aqueous bleaching solutions so that the resulting blue bleaching solutions do not have an adequate shelf life for a consumer product, and the formation of the blue bleaching solutions requires a dispersion agent to hinder precipitation.
Other existing methods achieve stable aqueous bleaching solutions by increasing the viscosities of these aqueous bleaching solutions. These methods aim at attaining a rheology that imparts elasticity or a false body to the aqueous bleaching solutions. However, these measures are temporary and are subject to chemical instability at higher levels of oxidants. Further, additives such as surfactant blends and polymer thickeners used to increase the viscosity may not be desirable, when, for example, a residue is not desired or the aqueous bleaching solutions are used for disinfecting food surfaces.
Colorants are normally understood in the art to include both pigments and dyestuff. Pigments refer mainly to inorganic salts and oxides, such as iron and chromium oxides, which are usually dispersed in crystal or powder form in an application medium. The color properties of the dispersion depends on the particle size and form of the pigment. Pigment colorants tend to be highly durable, heat stable, solvent resistant, lightfast, and migration fast. On the other hand, they also tend to be hard to process and have poor color brilliance and strength.
Dyes (also called dyestuffs) are conventionally understood to refer to organic molecules dissolved, as molecular chromophores, in the application medium. Examples are azo dyes, coumarin dyes, and perylene dyes. The color imparted by dyestuff to the resulting solution depends on the electronic properties of the chromophore molecule. Dyestuff colorants tend to have excellent brilliance and color strength, and are typically easy to process, but also have poor durability, poor heat and solvent stability, and high migration. They are also poorly bleach resistant being organic molecules bearing oxidant susceptible chemical groups, and generally fail to provide long lasting benefits to bleaching solutions.
Because of the contrasting properties of both types of colorants, much work has been done trying to improve the attributes of each class of colorant (see, for example, U.S. Pat. Nos. 4,017,476, 5,470,502, 5,710,197, 5,795,379, 5,871,872) and to combine the advantages of both into a single product (U.S. Pat. Nos. 4,486,237, 5,106,421, and PCT Publication WO 99/40123). These prior-art improvements have often involved binding dyes in a polymeric matrix to achieve greater color durability, improved heat and solvent stability, and to reduce migration as a result of the stable structure provided by the matrix.
More recently, U.S. Pat. No. 6,921,743 has described the use of some nanoparticles in combination with automatic dishwashing compositions where a halogen dioxide salt is electrolytically generated at time of use. However the materials are selected for suitability regarding surface modification of ceramic surfaces.
U.S. Pat. Pub. 2004/40156986 describes the use of colored nanopigments to provide a means for coloring compositions of matter that exhibit greater transparency than a coarse colored pigment, particularly in the visible wavelength range. However, the nanopigments employed are only adapted for use by incorporation into solid materials such as plastic, ceramic, cement. glass, wood, fibers, or in thickened coating materials such as paint and ink to be applied to a material surface in the form of a macroscopic film of the colored composition of matter.
In light of the foregoing discussion, there is a need for an aqueous bleaching solution that can be optically modified in a stable manner and that performs the functions of bleaching, whitening, brightening, and the like. The aqueous bleaching solution needs to include a stable dispersion an optically modifying material, and needs to be resistant to aggregation and settling. Further, the optically modified aqueous bleaching solution should be stable without the use of thickening agents, flocculants and dispersing agents.